Im not saying its right but I got 0,2π3,4π3,and2π f(x)=2cos2x−cosx−1=0
Solve this quadratic equation for cos x.
Since a + b + c = 0, use shortcut.
One real root is cos x = 1 and the other is cosx=ca=−12.
Trig table and unit circle -->
a. cos x = 1 --> arc x = 0, and arc x=2π
b. cosx=−12 --> arc x=±2π3
The arc −2π3 is co-terminal to the arc: 4π3
Answers for (0,2π):
0,2π3,4π3,and2π
